Color sensors are widely used to detect color for various systems. A color sensor generates a voltage output that represents the received color light. The output of a color sensor is typically connected to an analog to digital converter of a micro-controller, for example, which is employed to generate data for the system. Color sensors are utilized for ink detection, medical/life science applications, such as blood tests, camera calibration, and back light control system.
Unfortunately, many of the components of the color sensor, such as the resistors, and operational amplifier, are dependent on temperature. Ideally, the output of the color sensor maintains the identical behavior at other temperatures (e.g., 75 degrees Celsius, 100 degrees Celsius, 125 degrees Celsius). Unfortunately, although the relationship between the output and the incident light remains linear, the entire plot is typically shift up. This shift is referred to as “drift.” The drift can be partially attributable to leakage current that increases as temperature rises.
Drift is a major concern for designers of color sensors because one would prefer the behavior and operation of the color sensor to remain constant over the range of operating temperatures. As can be appreciated, unpredictable circuit behavior over temperature or a changing circuit behavior over temperature is not desirable.
FIG. 1 illustrates a prior art color sensor 2. The color sensor receives light 4 and generates a voltage output 6 that represents the amount of received light 4. FIG. 2 illustrates a first output versus light graph 6 for the color sensor at a first temperature and a second output versus light graph 8 for the color sensor at a second temperature of FIG. 1. By comparing the first graph 6 with the second graph 8, drift of the output versus light graph when the temperature increases from the first temperature to a second temperature is evident. It is noted that for the same amount of light received, the color sensor 2 when operating at the second temperature (e.g., 125 degrees Celsius) generates an output that is higher than the output generated by the color sensor 2 at the first temperature (e.g., 25 degrees Celsius). As noted previously, this behavior is not desirable.
Based on the foregoing, there remains a need for a temperature compensation method and apparatus for color sensors that addresses drift and that overcomes the disadvantages set forth previously.